The present invention relates to a two-component diazotype material comprising a support and a light-sensitive layer which comprises at least one diazonium compound which is derived from p-phenylenediamine and which carries a basic heterocyclic radical in the 4-position and ether groups in the 2- and 5-positions, respectively; a coupler component; and an acid stabilizer.
Two-component diazotype materials are known in the art which have a support provided with a light-sensitive layer comprising a diazonium compound, a coupler component, and an acid stabilizer. Upon exposure to actinic radiation, the diazonium compound is decomposed in the areas struck by light to form colorless compounds which are incapable of coupling. Developing of the two-component diazotype material is usually carried out with dry or moist ammonia gas. In the process, the acid stabilizer is neutralized and, simultaneously, the coupling reaction between the diazonium compound remaining in the areas not struck by light and the coupler component is initiated in these areas by a shift in pH in the light-sensitive layer.
It is also known that diazonium compounds derived from p-phenylenediamine and substituted in the 2- and 5-positions by ether groups have a high sensitivity to light in the spectral region at about 400 nm and are, in addition, particularly distinguished by their good stability and their coupling activity which is sufficient for many applications. These diazonium salts, moreover, couple with many coupler components to give strong and brilliant azo dyes of high optical density. Particularly suitable compounds are those which are substituted in the 4-position relative to the diazonium group by a heterocyclic radical, for example, a morpholino radical, and in the 2- and 5-positions by alkoxy groups having from 1 to 6 carbon atoms. These compounds are readily available, they couple, e.g., with blue components, to form strong azo dyes of a bright blue and a high visual density, and they undergo photolysis to form practically colorless decomposition products. Compounds of this kind include, for example, 4-N-morpholino-benzenediazonium salts which are substituted in the 2-and 5-positions by an alkoxy group having relatively long alkyl radicals, e.g., an n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, n-amyloxy, iso-amyloxy, hexyloxy, or cyclohexyloxy group. Compared with the 2,5-disubstituted dimethoxy and diethoxy compounds, these compounds have the additional advantage of a higher thermal stability and a greater coupling activity. In addition, the color shades of blue coupling dyes are shifted from a reddish to a greenish blue, with an increasing number of carbon atoms in the alkoxy group. Greenish blue azo dyes, in combination with orange-colored and brown azo dyes, result in neutral black color shades and are, therefore, particularly suitable for black formulations.
The stability and the coupling activity of a diazonium compound are, however, not only influenced by the diazonium salt cation, but also by the diazonium salt anion. In conventional sensitizing preparations, the diazonium compounds are present in the form of salts of inorganic acids, for example, hydrochloric acid, sulfuric acid, phosphoric acid, fluoboric acid, hexafluorophosphoric acid, or in the form of diazonium chloride double salts with zinc chloride, cadmium chloride, and stannic chloride. Due to their good solubility in water, the sulfates and the zinc chloride double salts are especially suitable for aqueous sensitizing preparations. Diazonium tetrafluoroborates and diazonium hexafluorophosphates are particularly employed for organic sensitizing preparations. The most frequently used diazonium chlorides, diazonium hydrogen sulfates, diazonium tetrafluoroborates, and diazonium chloride double salts with zinc chloride and cadmium chloride have the disadvantage that their thermal stability is relatively low and their coupling activity is too great. A two-component diazotype material which contains these diazonium salts in its light-sensitive layer develops at sufficient speed in most commercial duplicators, but has a markedly reduced storability. Diazonium hexafluorophosphates, on the other hand, have a substantially higher thermal stability than the aforementioned diazonium salts and diazonium chloride double salts, but exhibit considerable disadvantages in their coupling activity. A two-component diazotype material containing these diazonium hexafluorophosphates has a very good storability, but a slow developing speed, so that the maximally attainable optical density of such a diazotype material is obtained only after repeated developing. An absence of easy developing is, however, not acceptable for conventional duplicating.
It is a disadvantage of many of the highly light-sensitive two-component diazotype materials which are presently used in practice that these materials have an inadequate storability or cannot be developed at sufficient speed in the high-performance duplicators. Storability and ease of developing are incompatible so that, in a two-component diazotype material which has a good storability, developability is, as a rule, worse than in a material which has a limited storability. Good storability is particularly necessary in those cases in which the requirement for copies is small or in which the material is stored under extreme climatic conditions, for example, in a damp and warm tropical climate.